Cellular, or porous, materials have the ability to absorb significantly more energy than solid structures because of their ability to become denser (e.g., “densify”) in response to impacts. As such, cellular materials such as metallic or ceramic foams have been proposed as an energy absorbing layer in armor-type systems. However, the random microstructure of these materials severely diminishes their mechanical properties. The deformation of a cellular foam is dominated by the bending behavior of the cell struts. Simple mechanics dictates that bending dominated structures are less efficient in load carrying capacity than compression dominated behavior exemplified by a truss structure. Due this mechanical inefficiency, some fraction of the mass in the foam does not participate in energy absorption and represents added or parasitic weight.
U.S. Pat. Nos. 6,698,331 and 7,128,963, which are incorporated by reference herein in their entirety, propose blast protection material systems that incorporate random cellular ceramic or metallic foam as an energy absorbing layer. However, these patent disclosures do not provide an ordered micro-truss structure. The use of metallic lattice (truss) materials for energy absorbing application is discussed in U.S. Pat. No. 7,382,959 and U.S. patent application Ser. Nos. 11/801,908; 12/008,479; 12/074,727, 12/075,033, and 12/455,449 which are incorporated by reference herein in their entirety. Methods of manufacturing a micro-truss structure are described, for example, in U.S. patent application Ser. No. 12/455,449, which discloses a method of fabricating micro-truss structures having a fixed area, and 12/835,276, which discloses a method of continuously fabricating micro-truss structures according to a continuous process (e.g., a strip of arbitrary length), which are incorporated by reference herein in their entirety. However, there is still a demand for an impact or blast energy absorbing material that is light weight.
Compressible fluids have the ability to absorb a significant amount of energy. U.S. patent application Ser. No. 11/720,784, which is incorporated by reference herein in its entirety, describes a compressible fluid which may include a nanoporous material immersed in a non-wetting liquid which is compressed when external forces push the liquid into the nanopores of the material.
An explosive blast typically comprises an air pressure wave characterized by an overpressure P0 in excess of the ambient pressure Pa (and where P0/e and ti indicate that the pressure drops exponentially) with an associated impulse per unit area, as illustrated, e.g., in FIGS. 11a and 11b. In order for an intervening medium to protect a structure against the overpressure P0, the medium must reduce the pressure below the structure's damage threshold σth. This can be achieved by the intervening medium's undergoing a large volume decrease at a constant pressure, thereby extending the duration of the impulse.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person skilled in the art.